Electrical resistance heating element and process of making same



Apr. 3, 1923. 1,450,725

F. HODSON ELECTRICAL RESISTANCE HEATING ELEMENT AND PROCESS OF MAKING SAME Filed May 22, 1922 Patented Apr. 3, 1923.

UNITED STATES 1mm HODSON, or PHILADELPHIA, PENNSYLVANIA.

ELECTRICAL RESISTANCE HEATING ELEMENT AND PROCESS OF MAKING- Applicationjled May 22, 1922. Serial No. 562,568.

To all whom it may concem:

Be it known that I, FRANK HonsoN, a subject of the King of Great Britain, residing at Philadelphia, in the county of Philadelphia and State of Pennsyl ania, have invented certain new' and useful Improvements in Electrical Resistance Heating Elements and Process of Making Same, of which the following is a specification.

My present invention relates to electrical resistance heating elements and particularly to the kind made of amorphous or graphitic carbon capable of being used as heating agents in electric furnaces of various types.

One object of the present invention is to provide improved means for obviating the oxidizing of resistance elements. Another object is to make the mechanical "strength of such elements so as toenable the use thereof in a practical capacity within furnaces or the like.

Generally speaking the preferredprocess of making my improved elements consists in placing an electrical resistance heating element, such for example as a helical coil of graphite, in a suitable mold of anyshape' or design and ramming powdered or gran'u-- lar silicon-carbide, which has been previously mixed with a small proportion of suit able clay or other binding material, between the element and the mold to'give the desired thickness of silicon-carbide over the whole of the element. The mold may be made of any suitable material such for example as carborundum. The element is then heated either from an external'souroe or preferably by passing a current of electricity through the element until the element and its covering are heated to a temperature necessary to form the whole into, a solid mass; the element then being encased ina highly refractory and practically non-oxidizing envelope.

The envelope may be made absolutely impervious by glazing the surface with high temperature glaze. This may be carried out i by coating the mold with the glaze before ramming the silicon-carbide mixture.

Specifically speaking I attain the above mentioned objects in the following manner,

reference being had to the accompanying drawing in which Figure 1 is a side View of an electric resistance heating element made in accordance with my invention; the same being made out of graphite or other form of carbon including a helical coil,

Figure 2 is a view partly in longitudinal central section illustratin the element of Figure 1 enclosed in its highly refractory envelope, and

Figure 3 is a transverse section taken on the line 3-3 of Figure 2.

Referring to the drawing, the element 4 can be made by turning the same froma bar of graphite or other form of carbon to include a helically coiled portion 5 and screw threaded end portions 6 and 7. coiled portion 5 is placed within a mold such for example as a cylindrical mold 8 of carborundum as shown in Figures 2 and 3; said mold being of larger internal diameter than the external diameter of the helically coiled portion 5 of the element 4. The space between the convolutions ofsaid coiled portion and the spacebetween said coiled portion and the inner'surface of the mold 8 is then rammed with said silicon-carbide mixture illustrated at 9. If desired, rings 10 and 11 can be screwed on the end portions 6 and 7 to form an end abutment for the mold and silicon-carbide mixture. The structure thus formed is heated as above stated to a. temperature necessary to form the whole into a solid mass and the element 4 is then encased in ahighly refractory and practically non-oxidizing envelope. The structure The helically thus produced can be used as an electrical resistance heating means in which the electrio current can be utilized so as to pass through the element 4 taking the path of the helical convolutions of the coil 5; thus creating heat. At the same time oxidizing of the element is practically impossible and sufficient strength is imparted thereto to prevent the breaking down of the element during use.

While I have described my invention as taking a particular form, it will be understood that the various parts of my invention may be changed without departing from the spirit thereof, and hence I do not limit myself to the recise construction set forth, but consider tliat I am at liberty to make such changes and alterations as fairly come within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is 1. An electrical resistance heating element including a coil of carbon.

2. An electrical resistance heating element including a coil of graphite.

. fractory material.

8. An electrical resistance heating ele- 3. An electrical resistance heating element including a helical coil of carbon.

4. An electrical resistance heating element including a helical coil of graphite.

5. An electrical resistance heatmg element including a coiled portion of carbon.

enclosed in an envelope of highly refractory material.

6. An electrical resistance heating element including a coiled portion of graphite encased in an envelope of highly refractory material.

7.. An electrical resistance heating element including alhelically coiled portion of carbon enclosed in an envelope of highly rement including a helically coiled portion of graphite encased in an envelope of highly refractory material.

9. The process herein described consistmg of taking an electrical resistance element enc'asing said element in a non-oxidizing and highly refractory covering and then heating the same. a

- .10. The process herein described consisting of taking an electrical resistance element encasing said element in a non-oxidizing and highly refractory covering including silicon-carbide and then heating the same.

11 The process hereindescribed consisting of the placing of an electrical resistance heating element in a mold, then filling the space between said element and said mold with highly refractory material and then heating the structure thus formed. i

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

FRANK HODSON.

Witnesses:

A. EVERHARDT, HORACE DREVER, 

